1. Field of the Invention
The present invention relates to a movement simulator such as, for example, flight simulators, truck movement simulators, ship movement simulators, tank movement simulators and the like.
2. Background Information
Movement simulators are well-known in the art such as, for example, illustrated in European Patent Application No. EP-A-0 446 786 and U.S. Pat. No. 5,176,518 of the applicants. These patent applications disclose a flight simulator by means of which a user is subjected to the play of forces that occur in actual flight conditions. In this prior art the nominal accelerations are compared to a measured acceleration. The measured acceleration is calculated by multiplying the measured pressure differences in the two compartments of a hydraulic cylinder by the associated piston surface areas, subtracting this measured force from one another and dividing the obtained difference by an effective mass which is calculated by the computer. Difficulties from this system arise when the calculated effective mass is zero, thereby resulting in a non-defined situation which cannot be effectively handled by the simulator. The present invention overcomes the afore-mentioned difficulties of the prior art.
The invention relates to a movement simulator comprising:
a frame to be disposed fixedly and placed for instance on the ground; PA1 an auxiliary frame movable relative to that frame, for instance for carrying a control assembly and a seat for a user; PA1 at least one hydraulic or pneumatic cylinder which is coupled to the frame and supports the auxiliary frame, in which cylinder a piston is arranged for sliding sealingly, which piston divides the cylinder into two compartments; PA1 a central control unit connected to the or each cylinder for controlling the length thereof; and PA1 a sensor assembly for at least one parameter representative of the mechanical situation of the variable element, which sensor assembly supplies its output signals representative of the actual value of the relevant parameter to the central control unit for comparing thereof to the momentary nominal value of the relevant parameter and adjusting of the variable element until the actual value and the nominal value of the parameter are substantially the same as each other; PA1 which sensor assembly comprises an acceleration sensor which generates an acceleration signal representative of the acceleration of the end of the hydraulic or pneumatic cylinder connected to the auxiliary frame, which acceleration sensor comprises: PA1 two pressure sensors which generate pressure signals representative of the pressures prevailing in the two respective compartments; PA1 multiplying means for multiplying the pressure signals by the respective effective piston surface areas for generating respective force signals; PA1 first subtracting means which subtract these force signals from one another for generating an effective force signal; PA1 means for deriving an actual acceleration signal partly from this effective force signal; PA1 second subtracting means which subtract this actual acceleration signal and a nominal acceleration signal from one another to form an adjusting acceleration signal (partly) on the basis of which the cylinder is controlled.
The movement simulator according to the present invention is not limited to flight simulators but also embraces other applications wherein it is the desire to impose force, acceleration, speed and/or position on a movable auxiliary frame with great accuracy. A movement simulator can for instance also simulate the movements of tanks, trucks, ships or the like.
The above described European patent application EP-A-0 446 786, which is incorporated herein by way of reference, relates to a movement simulator which makes use of one or more hydraulic cylinders which are controlled such that a desired acceleration prescribed by a central control unit is followed as precisely as possible under different loads, that is, masses, on the hydraulic cylinders. For this purpose according to this prior art the nominal acceleration is compared to a measured acceleration. The measured acceleration was calculated by multiplying the measured pressure differences in the two compartments of the hydraulic cylinder by the associated piston surface areas, subtracting the thus measured forces from one another and dividing the obtained difference by a mass calculated by the computer.
It has been found that conditions can occur in which it is possible for the calculated masses to obtain a negative value. Mathematically and physically this does indeed appear to be correct. Acceleration and force can in some conditions possess an opposite sign.
Resulting however from the transition from a positive to a negative mass and vice versa is a non-defined situation which can be designated mathematically as "dividing by zero" in the calculation of the acceleration.
The present invention has for its object to resolve this problem and provides to this end a movement simulator of the described type having the feature that the acceleration circuit further comprises
a third subtracting circuit which subtracts the effective force signal and an estimated force signal from one another to form an actual force signal; and
adjustable amplifying means for amplifying this actual force signal with a desired factor, the output signal of which amplifying means is the actual acceleration signal.
The difference between the present invention and the said prior art is that the computer calculates an estimated force instead of an estimated mass. This estimated force is compared to the measured force which is determined in the manner already described from the measured pressure differences. The desired acceleration generated by the computer is corrected with the difference between the measured force and the calculated force. The simulator according to the invention therefore makes use as it were of a force loop which is controlled by the estimated force.
The invention will now be elucidated with reference to the annexed drawing. Reference is also made to the older European patent application EP-A-0 446 786 of applicant, in which are stated per se known further special features of movement simulators of the present type.